1. Field
The following description relates to a passive optical network (PON), and more particularly, to technology for increasing a transmission distance and the number of splits in the passive optical network.
2. Description of the Related Art
A time division multiple access passive optical network (TDMA-PON) is broadly classified as an EPON (Ethernet PON) or a GPON (Gigabit-capable PON). Currently, this technology corresponds to next generation-PON (NG-PON1) technology, which is a 10 Gbps-class TDMA-PON, and 10G-EPON and XG-PON1 (10 Gigabit-capable PON) technologies are standardized.
The ITU-T SG15 standardization group has selected time and wavelength division multiplexed passive optical network (hereinafter referred to as ‘TWDM-PON’) technology, which is 40 Gbps-class NG-PON2 technology, as standardization technology. The TWDM-PON is technology for providing a broadband service to subscribers using previously standardized XG-PON1 and wavelength multiplexing technology. That is, a transmission rate of 10 Gbps downstream and 2.5 Gbps upstream is supported per wavelength division multiplex (WDM) wavelength. Optical network units (hereinafter referred to as ‘ONUs’) may provide a service to subscribers by selecting an arbitrary wavelength according to wavelength control from an optical line terminal (hereinafter referred to as ‘OLT’) using wavelength tunable technology.
A general TWDM-PON link supports four types of XG-PON1 technology for one OLT and supports a transmission rate of 10 Gbps downstream and 2.5 Gbps upstream for each wavelength. In this case, wavelength signals use a fixed wavelength band. In a signal transmission process of the general TWDM-PON link, wavelength signals having four fixed wavelength bands are transmitted through a wavelength multiplexing and de-multiplexing device of the OLT using one optical line. These wavelength signals are respectively transmitted to the ONUs through an optical splitter in a remote node. The ONU receives the signal having a wavelength selected from among four wavelengths and provides a service to subscribers. For this purpose, the ONU may use a wavelength tunable light source.
The general TWDM-PON link supports a transmission rate of from 625 Mbps to 10 Gbps downstream and from 156 Mbps to 5 Gbps upstream per subscriber with a split ratio of 1:64. However, it is inefficient to apply in a subscriber network in terms of costs. That is, when expensive 40 Gbps TWDM-PON equipment is used in a previously installed optical distribution network (hereinafter referred to as ‘ODN’), effectiveness of a transmission service decreases due to a small number of subscribers. Therefore, in order to increase the number of subscribers per port of the 40 Gbps TDMA-PON equipment while the existing ODN is directly accommodated, a reach extender capable of providing long-distance transmission and a high split ratio in a 40 Gbps TWDM-PON link is necessary.